Exchangeable processing means for barking machines of the type mentioned by way of introduction are subjected to great loads during barking, and it is thus most important for these to be fixed in such manner that there is no risk of their coming loose during barking. The rotator normally rotates at high speed, and a processing means which comes loose may therefore cause great damage. The processing means are subjected, inter alia, to forwardly directed forces when shearing off bark from a log, to rearwardly directed forces after the swinging arm has been pivoted away from the log surface because of an irregularity in the circumferential surface of the log and is again pivoted inwards at high speed and hits the log surface, and to laterally directed forces in the direction of feed of the logs when they are hit by the end surface of logs arriving at the barking machine.
Since, after being used for some time, the processing means become worn and are rejected to be replaced by new ones, it is desirable that they be as inexpensive as possible. On the one hand, they should have as small dimensions as possible for a given length of the barking processing edge so that the volume of material becomes small and, on the other hand, they should be as easy as possible to manufacture. As a rule, the processing means are manufactured by forging a blank to a suitable shape and size and finally machining this by milling. From the viewpoint of cost, it is advantageous for the forged blank to have a shape which conforms as well as possible with the finished processing means, so that only a small amount of material need be removed in the final machining. Moreover, it will be time-saving and reduce the number of machining steps if the finished processing means has as simple a geometric shape with as large and continuous planar surfaces as possible and straight edges between the surfaces.
An individual processing means is usually fixed by means of a single bolt which is passed through the same and the swinging arm. In most cases, it is desirable to use a bolt having as small a diameter as possible, and therefore the processing means and the swinging arm are designed so that the bolt needs to absorb only tensile forces which are directed perpendicular to the upper and lower surfaces of the processing means. These forces are relatively small and give rise to pure tensile forces which a bolt is well suited to manage. On the other hand, the forwardly, rearwardly and laterally directed forces are considerably greater. To prevent deformation and any fracture of the bolt or turning round the same, the processing means and the seats of the swinging arms are designed in such manner that these forces are absorbed by the swinging arms.
This is accomplished in certain types of processing means by mounting them in cup-shaped seats of the swinging arms. Processing means of the type mentioned by way of introduction, however, have the advantage that, for instance, they can be made with smaller dimensions for a given length of the barking edge, With a view to absorbing forwardly, rearwardly and laterally directed forces, they are formed with a supporting surface which is directed backwards or, preferably, obliquely backwards and which is adapted to abut against a swinging arm supporting surface which is directed forwards or obliquely forwards against the direction of feed of the logs, and some sort of engaging means between the lower surface of the processing means and the seat of the swinging arm.
It is previously known to design the engaging means as, for instance, a projection with an elongate, rounded shape in the area round the fixing bolt, as disclosed in, for instance, SE 463,660 and the US counterpart U.S. Pat. No. 4,852,622, which engages a correspondingly formed recess in the seat of the swinging arm. With such an engaging means, a deep and complicated machining is required of the processing means as well as the swinging arm.
It is also known from SE 9703183-5 to bore a hole in the lower surface of the processing means as well as in the seat of the swinging arm and arrange a pin in the holes to prevent turning of the processing means in relation to the swinging arm. Such an engaging means certainly yields relatively little and simple machining, but is felt by the users to be complicated in dismounting of worn processing means and mounting of new ones. On the one hand, they can get stuck by pinching owing to rests of trees being wedged between the processing means and the swinging arm, which makes the processing means so difficult to dismount that they must be knocked away and, on the other hand, they can be difficult to fit during mounting.